“Like many people he has an annual check up from an external provider – if he ever needs to see a doctor for anything it is with his local GP, or with other NHS services,” a spokesperson told City A.M..

This admission came after Livingstone defended his health in the face of criticism that he was not up to the job of running for Mayor.

"I've lost a stone during this campaign, and I went for my annual medical last week and my doctor almost had an orgasm because I'm so fit," he said.

Livingstone was responding to claims by Labour MP Austin Mitchell that his campaign was "tired". Mitchell told HuffPost UK that Livingstone "no longer [has] the hint of danger that used to surround him."

A spokesperson for Tory Mayor Boris Johnson said: “This is yet another example of Ken Livingstone’s hypocrisy – saying one thing but does another.

"First we discover that at the same time as attacking tax avoiders, saying they shouldn’t be allowed to vote in elections, he is avoiding tax himself and standing in an election.

"Now we learn that while campaigning as a defender of the NHS he uses private healthcare. How can Londoners believe anything this man says?”